1. Field of the Invention
The present invention generally relates to a method of controlling a re-emission interval of an asynchronous transfer mode interval controller and, more particularly, a method of controlling a re-emission interval using a theoretical departure time.
2. Description of the Prior Art
Generally, in developing public telecommunication network, a user requires gradually increased speed, a wide-band, and multiple functions, and increased intelligence regarding service such as multimedia, etc. Today, B-ISDN has been developed for wide band communication. Since international standard organization such as ITU-T and ATM-Forum have recommended ATM as a wide band communication mode, an ATM switching system is being devloped.
However, traffic control is essential in using an ATM system because the user information therein is transferred in an ATM cell and an asynchronous method is utilized. To maintain the quality of service for the connected calls, there is call admission control for determining whether a new call is accepted, priority control for recognizing a sensibility degree for transfer delay and cell loss among various kinds of cells and preferentially transferring and discarding calls, congestion control for controlling flow so that a blocking state is not maintained for a long time when congestion occurs and for preventing congestion in network node, Usage Parameter Control(UPC)/Network Parameter Control(NPC) for protecting a network source by monitoring a traffic characteristic agreed upon between a user and a network and discarding a cell when the agreement is violated, and a cell interval control for efficiently using the network resource by controlling cell interval and equalizing burst traffic.
There are conventional cell interval control methods such as an Arrival Re-emission Time(ART) method based on the input time in an interval controller, and a Recent Departure Time(RTD) method based on the output time from an interval controller.
The ART method described above have a simple buffer control dealing with multiplexing in an interval controller but having an effect on a multiplexed cell stream in output traffic by taking the input state into consideration without taking output state from the interval controller into consideration. Delay which is generated between every cell varies because of the multiplexing of the interval controller, as indicated by cell delay variation(CDV). Accordingly, in an ART mode, there is declined performance of an interval control function due to the multiplexing of the interval controller. The multiplexing output cell stream in the interval controller is affected by the utilization of link and, consequently in the context of network resource management, stable interval control is difficult. On the other hand, the Recent Departure Time(RDT) method performs control based on the output time of the interval controller. By including CDV generated from the interval controller, it is possible to control a distinctive cell interval. However, in RDT method, when counting the expectation departure time, the actual departure time of the previous cell is used at the interval controller. After this registered cell with the scheduled departure time has a little queuing delay, it departs from the interval controller later than the scheduled time. As such the departure time is used for determining the scheduled departure time of the next input cell, the queuing delay is accumulated according to sequential cell processing. Therefore, this requires theoretically unlimited buffers.
Accordingly, the present invention suggests a method of controlling a cell interval in order to reduce delay from the interval controller, which has stable characteristics for the connecting number and the utilization of a link and is unsensitive to CDV by applying the advantage of RDT mode and compensating for the shortage thereof, and therefore uses a Theoretical Departure Time(TDT) for controlling the cell re-emission interval.